The present invention relates to a polycarbonate resin composition, particularly the one having excellent sliding properties.
Recently, for the purpose of expediting size and weight reduction or decrease of the number of parts of OA equipment and electronic devices in general, use of synthetic resins for the sliding members is prevailing. Among such synthetic resins, polycarbonate resins are favorably used for the parts of the sliding members such as gears because of their excellent dimensional precision and mechanical strength.
Usually, for improving the sliding properties, a sliding material is added to the polycarbonate resins. For instance, Japanese Patent Application Laid-Open (KOKAI) No. 63-213555 discloses a resin composition comprising a polycarbonate resin and ethylene tetrafluoride resin. Such a resin composition, however, has a problem that it tends to cause delamination or mold deposit during the molding operations because a large amount of a fluorine resin having no miscibility must be used. Japanese Patent Application Laid-Open (KOKAI) No. 4-136065 discloses a resin composition comprising polybutylene terephthalate and a polycarbonate. This resin composition involves a problem that not only the excellent properties (mechanical strength, heat resistance and flame retardancy) inherent to the polycarbonate resins are impaired but there also is a risk of phase separation taking place during molding.
Further, a resin composition produced by blending a silicone oil in a polycarbonate resin has been proposed. In the case of this composition, there is a problem that the article surface becomes tacky to spoil the sliding properties because the silicone oil in the surface of the molded article oozes out in a short time. As a solution to this problem, use of a high-molecular weight silicone oil has been proposed. In this case, however, as it is necessary to add a large quantity of silicone oil for obtaining satisfactory sliding properties, there tends to arise problems such as non-uniform glossiness of the molding surface due to phase separation of the silicone oil in the surface of the molded article, so that this resin composition is unsuited for practical use.
Further, Japanese Patent Application Laid-Open (KOKAI) No. 9-255864 provides a polycarbonate resin composition in which a high-viscosity dimethyl silicone oil and a polyolefin, polystyrene, acrylonitrile-styrene resin or acrylonitrile-butadiene-styrene resin are added to a basic polycarbonate resin for improving miscibility between the polycarbonate resin and the silicone oil. This polycarbonate resin composition, however, is not always satisfactory in balance of mechanical properties, molded article appearance and sliding properties.
As a result of the present inventors"" earnest studies to solve the above problem, it has been found that by blending a silicone oil having specific dynamic viscosity and a rubber component having a specific structure with a polycarbonate resin, the obtained resin composition has excellent sliding properties without imparting the inherent properties of polycarbonate resin.
The present invention has been attained on the basis of the above finding.
The object of the present invention is to provide a polycarbonate resin composition having excellent sliding properties and capable of providing good appearance to its molded articles without impairing the inherent properties such as mechanical strength and heat resistance of the polycarbonate resins.
To attain the above aim, in the first aspect of the present invention, there is provided a polycarbonate resin composition comprising 100 parts by weight of a polycarbonate resin, 0.05 to 5 parts by weight of a silicone oil (BH) having a dynamic viscosity of not less than 10,000 m2/s at 25xc2x0 C., and 0.5 to 25 parts by weight of a composite rubber (C) having such a structure that the polyorganosiloxane rubber component and the polyalkyl (meth)acrylate rubber component are interlocked to form a unitary composite (intertwined with each other).
In the second aspect, there is provided a polycarbonate resin composition comprising:
100 parts by weight of a polycarbonate resin;
0.05 to 5 parts by weight of a mixture of silicone oil (BH) having a dynamic viscosity of not less than 100,000 mm2/s at 25xc2x0 C. and a silicone oil (BL) having a dynamic viscosity of less than 100,000 mm2/s at 25xc2x0 C., with the BH/BL ratio by weight being defined to be 2/1 to 200/1; and
0.5 to 25 parts by weight of a composite rubber (C) having such a structure that the polyorganosiloxane rubber component and the polyalkyl (meth)acrylate rubber component are interpenetrated with each other.
The present invention is described in detail below.
As the polycarbonate resin (A) (which may hereinafter be referred to as a xe2x80x9cPC resinxe2x80x9d) usable in the present invention, there exemplified aromatic PC resins, aliphatic PC resins, and aromatic/aliphatic PC resins. Of these resins, aromatic PC resins are preferred. Examples of such aromatic PC resins include thermoplastic aromatic polycarbonate polymers or copolymers which may be branched, which can be obtained by reacting an aromatic hydroxyl compound or this compound and a small quantity of a polyhydroxyl compound with phosgene or a carbonic acid diester. The preparation method of these PC resins is not specified in the present invention; the conventional methods such as phosgene method (interfacial polymerization method) and melting method (ester exchange method) can be used. It is also possible to use aromatic PC resins produced by the melting method, with the number of the terminal OH groups being properly adjusted.
Examples of the aromatic dihydroxyl compounds usable for the above reaction include 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), tetramethylbisphenol A, bis(4-hydroxyphenyl)-p-diisopropylbenzene, hydroquinone, resorcinol, 4,4-dihydroxydiphenyl and the like. Of these compounds, bisphenol A is preferred. It is possible to use compounds having at least one tetraalkylphosphonium sulfonate combined with the said aromatic dihydroxyl compounds and/or polymers or oligomers having a siloxane structure and containing phenolic OH groups at the terminal for the purpose of further enhancing flame retardancy.
For obtaining a branched aromatic PC resin, a polyhydroxyl compound such as phloroglucin, 4,6-dimethyl-2,4,6-tri(4-hydroxyphenyl)heptene-2,4,6-dimethyl-2,4,6-tri(4-hydroxyphenyl)heptane, 2,6-dimethyl-2,4,6-tri(4-hydroxyphenyl)heptene-3,1,3,5-tri(4-hydroxyphenyl)benzene and 1,1,1-tri(4-hydroxyphenyl)ethane; 3,3-bis(4-hydroxyaryl)oxyindole (isatinbiphenol), 5-chloroisatin, 5,7-dichloroisatin, 5-bromoisatin or the like is used as part of the aromatic dihydroxyl compound mentioned above. Such an additive compound is used in an amount of usually 0.01 to 10 mol %, preferably 0.1 to 2 mol %.
The monovalent aromatic hydroxyl compounds can be used for modifying the molecular weight. Examples of such monovalent aromatic hydroxyl compounds include m- and p-methylphenol, m- and p-propylphenol, p-tert-butylphenol and p-long-chain alkyl substituted phenol.
As the aromatic PC resin, it is preferable to use the PC resins derived from 2,2-bis(4-hydroxyphenyl)propane or the PC copolymers derived from 2,2-bis(4-hydroxyphenyl)propane and other aromatic dihydroxyl compounds. They may be copolymerized with a polymer or oligomer having a siloxane structure for further enhancing flame retardancy. Two or more different types of aromatic PC resin may be used as a mixture.
The viscosity-average molecular weight of the PC resin used in the present invention, as calculated by conversion from the solution viscosity measured at 25xc2x0 C. using methylene chloride as solvent, is usually in the range of 16,000 to 30,000. If the viscosity-average molecular weight is less than 16,000, the produced composition may be poor in mechanical strength, and if the viscosity-average molecular weight exceeds 30,000, the articles molded from the composition tend to become defective in appearance. The preferred range of the viscosity-average molecular weight of the PC resin used in the present invention is 17,000 to 25,000, more preferably 18,000 to 23,000.
It is essential that the silicone oil (BH) used in the present invention has a dynamic viscosity of not less than 10,000 mm2/s measured at 25xc2x0 C. If the dynamic viscosity of the silicone oil (BH) measured at 25xc2x0 C. is less than 10,000 mm2/s, it may be difficult to retain the sliding properties for a long time. The dynamic viscosity of the silicone oil (BH) measured at 25xc2x0 C. is preferably not less than 100,000 mm2/s, more preferably not less than 500,000 mm2/s, even more preferably not less than 1,000,000 mm2/s.
In the present invention, the content of silicone oil (BH) is 0.05 to 5 parts by weight based on 100 parts by weight of the PC resin (A). If the silicone oil content is less than 0.05 part by weight, the composition may be unsatisfactory in sliding properties, and if the said content exceeds 5 parts by weight, there can not be obtained a good appearance of the molded article. The silicone oil content is preferably 0.1 to 4 parts by weight, more preferably 0.2 to 3 parts by weight based on 100 parts by weight of the PC resin (A).
In case where the silicone oil (BH) having a dynamic viscosity of not less than 100,000 mm2/s is used, it is preferable to use a silicone oil (BL) having a dynamic viscosity of less than 100,000 mm2/s at 25xc2x0 C. along with the said silicone oil (BH), with the BH/BL ratio by weight being defined to be 2/1 to 200/1, because the specific wear loss can be reduced by the combined use of such two types of silicone oil.
In case of the combined use of such two types of silicone oil, the dynamic viscosity of the silicone oil (BH) at 25xc2x0 C. is preferably not less than 500,000 mm2/s, more preferably not less than 1,000,000 mm2/s. The dynamic viscosity of the silicone oil (BL) at 25xc2x0 C. is preferably not more than 50,000 mm2/s, more preferably not more than 10,000 mm2/s. The BH/BL ratio by weight is preferably 5/1 to 150/1, more preferably 10/1 to 100/1. A too high ratio of the silicone oil (BH) tends to reduce wear resistance of the composition and also may give adverse effect to the appearance of the molded article. Also, a too high ratio of the silicone oil (BL) tends to lower wear resistance of the composition and may make the molded article too tacky.
The silicone oils used in the present invention are not specified but can be properly selected from the known ones as far as they meet the above-defined conditions of dynamic viscosity. For instance, it is possible to use silicone oils comprising polydimethylsiloxane, silicone oils in which the methyl groups of polydimethylsiloxane are partly or entirely substituted with phenyl group, hydrogen, alkyl group having 2 or more carbon atoms, halogenated phenyl group or fluoroester group, epoxy-modified silicone oils having epoxy groups, amino-modified silicone oils having amino groups, alcohol-modified silicone oils having alcoholic hydroxyl groups, and polyether-modified silicone oils having a polyether structure. These silicone oils can be used either singly or as a mixture of two or more of them. In case of using a silicone oil (BL) of low dynamic viscosity in combination with a silicone oil (BH) of high dynamic viscosity as mentioned above, the silicone oil (BL) is preferably selected from those having phenyl groups.
In the present invention, a composite rubber (C) having such structure that the polyorganosiloxane rubber component and the polyalkyl (meth)acrylate rubber component are interlocked (intertwined) with each other, is used. In such a composite rubber (C), a polymer having the repeating units selected from dimethylsiloxane, diphenylsiloxane and methylphenylsiloxane is used as the skeleton of the polyorganosiloxane rubber component. On the other hand, as the skeleton of the polyalkyl (meth)acrylate rubber component, a polymer having the repeating units selected from methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate is used.
Emulsion polymerization is preferably used as the method of producing the composite rubber (C) in the present invention. First, a latex of polyorganosiloxane rubber is prepared, then a monomer for synthesizing alkyl (meth)acrylate rubber is interpenetrated in the particles of the polyorganosiloxane rubber latex, and then the monomer is polymerized.
The polyorganosiloxane rubber component/polyalkyl (meth)acrylate rubber component ratio by weight is usually 90/10 to 20/80, preferably 85/15 to 30/70, more preferably 80/20 to 40/60. If the ratio of the polyalkyl (meth)acrylate rubber component is below the above-defined range, its miscibility with the PC resin becomes too low, causing deterioration of appearance of the molded article, while if the said ratio exceeds the above-defined range, the improving effect of sliding properties may be unsatisfactory.
A vinyl monomer may be graft-polymerized to the composite rubber (C). Various types of vinyl monomers, for example, aromatic alkenyl compounds such as styrene, acrylic esters such as methyl methacrylate, and vinyl cyanide compounds such as acrylonitrile can be used either singly or as preferable combinations. Such a composite rubber (C) is easily available as it is commercially sold, for instance, under the trade name of xe2x80x9cMETABLENxe2x80x9d by Mitsubishi Rayon Co., Ltd. The above mentioned method is described in detail in U.S. Pat. No. 4,888,388, but the method producing the composite rubber (C) is not limited to the above described method.
The content of the composite rubber (C) is 0.5 to 25 parts by weight based on 100 parts by weight of the PC resin (A). If the composite rubber (C) content is too low, the improving effect of sliding properties may be unsatisfactory, and if the content is too high, the composition deteriorates in mechanical strength. The (C) content is preferably 0.8 to 20 parts by weight, more preferably 1 to 15 parts by weight based on 100 parts by weight of the PC resin (A).
The silicone oil (BH)/composite rubber (C) ratio by weight is usually 5/1 to 1/50, preferably 2/1 to 1/30. If the BH/C ratio is outside the above-defined range, the composition may be low in mechanical strength and/or appearance of the molded article may be deteriorated.
The PC resin composition of the present invention may contain, if necessary, stabilizers such as ultraviolet absorber and antioxidant, additives such as pigment, dye, lubricant, flame retardant and release agent, reinforcements such as glass fiber, glass flakes and carbon fiber, whiskers such as those of potassium titanate and aluminum borate, and the like.
Also, in the PC resin composition of the present invention, it is possible to blend other thermoplastic resin(s) than the PC resins for the purpose of improving performance qualities such as moldability and chemical resistance of the composition. The kind and the content of such other thermoplastic resin(s) can be properly selected. Examples of such other thermoplastic resins include polyester resins, polyamide resins, polyolefin resins, polyphenylene ether-based resins, styrene-based resins, polysulfone, polyether sulfone, polyphenylene sulfide, polyarylates, polyamide-imide, polyether-imide and the like.
The polyester resins usable for the said purpose include polybutylene terephthalate, polyethylene terephthalate, polybutylene naphthalate and polyethylene naphthalate. The polyolefin resins include polyethylene and polypropylene. The polyphenylene ether-based resins include a polyphenylene ether resin and a mixture of polyphenylene ether, polystyrene and/or HIPS. The styrene-based resins include polystyrene, HIPS (high impact-resistant polystyrene), AS (acrylonitrile-styrene) resin and ABS (acrylonitrile-butadiene-styrene) resin.
The amount of the other thermoplastic resin(s) blended in the PC resin is usually less than 50% by weight, preferably not more than 40% by weight, more preferably not more than 30% by weight, based on the combined amount of the PC resin and the other resin(s). The lower limit is usually 1% by weight.
For producing the PC resin composition of the present invention, it is possible to use, for instance, a melt mixing method in which the components described above are blended and mixed by various types of mixing means such as single- or multi-screw mixer, Banbury mixer, roll mill, Brabender Plastograph, etc., and then cooled and solidified, or a solution mixing method in which the said components are added to a preferable solvent, for example, a hydrocarbon such as hexane, heptane, benzene, toluene, xylene, or a derivative thereof, and the dissolved components are mixed together, or the dissolved components and the undissolved components are mixed in a suspended state. The melt mixing method is advantageous in terms of cost.
The method of molding the PC resin composition of the present invention is not specified; the various molding methods commonly used for the molding of the thermoplastic resin compositions, such as injection molding, blow molding, extrusion molding, sheet forming, thermoforming, rotational molding, laminate molding, etc., can be used.
The PC resin composition according to the present invention has excellent Izod impact strength, flexual modulus of elasticity, flexural fatigue failure, heat resistance and sliding properties and is capable of providing good appearance of the molded articles, so that it is useful for the manufacture of various kinds of sliding members such as gears. Thus, the present composition is of high industrial value and finds its wide scope of use, for instance in the fields of electrical and electronic devices and parts of OA equipment.